Allo-Threonine

Extension of this strategy enables syntheses of both protected c-threonine and t-allo-threonine, in which reagent-controlled stereoselecdve epoxidadon of a common intermediate is the key step fScheme 4.8. " ... 

The L-threonine (EC 4.1.2.5), D-threonine (EC 4.1.2.-) or L-allothreonine aldolases (EC 4.1.2.6 synonymous to S1IMT) can be used for resolution of racemic (allo)threonine mixtures by highly selective cleavage of the unwanted isomers42, but can also efficiently direct the anabolic pathways. The substrate spectrum includes propanal, butanal and dodecanal43. 

High-pressure [4 + 2] cycloaddition of 1-methoxy-1,3-butadiene to A/,0-protected D-threoninals and D-allo-threoninals [91]... 

Examination under long-wavelength UV light (X, = 365 nm) reveals pink to brilliant red fluorescent chromatogram zones on a dark background for threonine and allo-threonine. 

TABLE 8.11. CYCLIZATION OF THREONINE AND ALLO-THREONINE PEPTIDES UNDER MITSUNOBU CONDITIONS"... 

L-Threonine [72-19-5] M 119.1, m 251-253°, [a]] -28.4° (H20). Likely impurities are allo-threonine and glycine. Crystd from water by adding 4 volumes of EtOH. Dried and stored in a desiccator. 

The stereochemistry of the N-methyl-alanine residue connected to the end of the 3-hydroxy-2,4,6-trimethylheptanoic acid moiety as well as of the allo-threonin placed between the L-methylglutamine and L-threonin residues have been revised to the correct actual stereostructure of callipeltin A (57) [104]. Two additional members of this class, named callipeltins D and E, have been isolated from... 

Threonine contains a sterically hindered and therefore less reactive hydroxy group. The O-acylation of unprotected threonine during coupling reactions is therefore less problematic, but can nevertheless occur. Noncoded hydroxy amino acids containing a secondary hydroxy group have a reactivity similar to threonine. These hydroxy amino adds contain an additional asymmetric center at the (3-carbon atom. In the case of reactions on the secondary hydroxy group, this center is accessible to racemization, e.g. threonine can be converted into allo-threonine. 

W. Stbcklein and H.-C. Schmidt, Evidence for L-threonine cleavage and allo-threonine formation by different enzymes from Ciostridium pasteurianium Threonine aldolase and serine hydroxymethyltransferase, Biodiem. ]., 232 621 (1985). 

A. Golfbiowski and J. Jurczak, The cyclocondensation reaction of 1-benzoyIoxy-2-fert-butyldimethylsilyloxy-4-methoxy-1,3-butadiene with N,0-protected o-threoninals and D-allo-threoninals. Tetrahedron 47 1045 (1991). 

Properties Colorless crystals, ((//-threonine) Mp 228-229C with decomposition (/(-)-threonine) (naturally occurring) mp 255-257C with decomposition ((/Z-allo-threonine), mp 250-252C. Soluble in water. Optically active. 

Phe, phenylalanine alloThr, allo-threonine Ala, alanine Figure 3.2 Structures of mycobacterial lipids. Reproduced with permission from Harwood and Russell (1984). 

A different synthetic route converted alanine to the diasteromcric mixture of oxazoIidin-2-ones, S.lla and S.llb. After separation of these diastereomers, oxidative cleavage of the alkene moiety in S.IIa (with RuCla and NaI04) led to S.12a and basic hydrolysis gave D-isothreonine S.ISa). L-allo-Threonine (S.J3b) was formed in a similar manner from diastereomer 5,1 Ib, via 5.12b. Note that a variety of amino acids were prepared from alanine. These include both 2-amino, 3-amino, and 4-amino acid derivatives. 

Model reactions of this type have been studied in which the catalyst is pyridoxal plus a metal. The enzymatic reactions all appear to use pyridoxal phosphate as a cofactor, and in the case of a bacterial system, Mn" is also required. A major difference between the enzymatic and the model reactions is the requirement for a folic acid cofactor in the former. The formation of glycine and acetaldehyde from L-threonine and L-allo-threonine has been described by Lin and Greenberg. Their partially purified enzyme, threonine aldolase, was not shown to require any cofactors, and the reaction was not reversed. This is in contrast to the results of nonenzymatic experiments in which pyridoxal and a metal catalyze the reversible cleavage of threonine. 

Under mildly basic conditions complexes such as [Co(en)2(gly)] react with simple aldehydes thus acetaldehyde gives rise to threonine and allo-threonine [equation (12)] in proportions depending on the pH of the... 

Zhao H, Hamase K, Morikawa A, Qiu Z, Zaitsu K. Determination of d- and 1-enan-tiomers of threonine and allo-threonine in mammals using two-step high-performance liquid chromatography. J Chromatogr B Anal Tech Biomed Life Sci... 

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